1. Field of the Invention
The present invention relates to air pressure indicators and, more particularly, to an air pressure indicator incorporated into the valve stem cap of a tire.
2. Description of the Background
Proper tire inflation requires that the correct air pressure be maintained in the tire, and is important for achieving optimal fuel efficiency and increasing tire life. Under inflated tires can result in fast and excessive wear on the outside of the tread as well as improper vehicle handling. Over inflated tires can result in fast and excessive wear on the middle part of the tread and are more rigid, possibly leading to a blowout.
A common method for monitoring tire air pressure involves manually removing the valve cap and applying a tire gauge to the valve stem. This method poses several hardships for the operator. First, the method is complicated by the need for an additional tool, the tire gauge, which may be unavailable when needed and must be purchased at an additional cost to the operator. Second, the operation is time consuming for the operator as he must remove the valve stem cap for each tire, apply the tire pressure gauge, and re-fasten the valve stem caps. Finally, the process exposes the operator to brake dust and road dirt which naturally accumulate on tire valves.
There have been past efforts to develop air pressure indicators incorporated into the valve stem cap of a tire. For example, U.S. Pat. No. 6,374,666 to the inventor named herein discloses a tire pressure gauge apparatus that may be secured to the valve stem in a vehicle tire. A pressure indicator element displays a pressure reading of received air from within the tire which varies with the position of a pressure equilibration structure so that alteration of the pressure of received air within a received air chamber from the valve stem causes movement of the equilibration structure within the housing to re-establish pressure equilibrium between biasing air sealed within the biasing air chamber and received air within the received air chamber, and movement of the equilibration structure causes the indicator element to move relative to the housing to provide a received air pressure reading.
U.S. Pat. No. 5,929,330 to Ford discloses a pressure gauge that provides a simple, efficient and highly visual indication of pressure change from a normal condition to various abnormal conditions.
U.S. Pat. No. 5,569,849 to Cummings discloses a visual tire cap pressure gauge for visually indicating when air pressure within the tire drops below a set point, so as to enable a person at a glance to tell if the tire needs more air.
U.S. Pat. No. 5,115,832 to Higdon et al. provides visual indication of under-inflated condition.
U.S. Pat. Nos. 4,606,391 and 4,819,686 to Achterholt discloses a valve cap adapted to be screwed onto the valve of a pneumatic tire to provide a pressure drop indication.
U.S. Pat. Nos. 4,520,664 and 5,027,740 to Kramer disclose a tire pressure indicator for visual observation of tire pressure including a screw-on cartridge containing a spring-biased piston with a movable shield which covers a central indicator pilot when tire pressure is up to requirements. When pressure is below what it should be, the piston retracts to allow the shield to expose indicator pilot to the view of an observer, thus serving as a warning that inflation is required.
U.S. Pat. No. 4,480,580 to Nalence discloses a low tire pressure warning device which includes a housing, a bladder and/or spring loaded piston within the housing and a colored warning streamer. The bladder, upon contraction, axially moves a spring-loaded piston so as to “pop out” the colored warning streamer.
U.S. Pat. No. 4,464,929 to Willis discloses a tire cap pressure gauge for mounting upon a tire valve stem and measuring tire pressure that has a housing, a manually operated plunger extending axially through the housing, a spring extending about the plunger, a piston biased by the spring and having indicia. The housing has multiple windows with indicia proximate thereto for viewing the position of the piston.
U.S. Pat. No. 4,362,121 to Pegram discloses a deflation warning device for a pneumatic tire which gives a clear, positive indication of a predetermined pressure loss by the exposure of a brightly colored element within a transparent dome.
U.S. Pat. No. 4,174,673 to Tung et al. discloses a low pressure warning cap for a pneumatic tire air valve including a threaded connector for attachment to a conventional air valve stem.
U.S. Pat. No. 4,079,691 to Curado discloses a tire pressure indicator that uses a poppet. When the pressure in the tire drops to a predetermined level, the poppet moves to a second position releasing air into the cap. An indicating element normally concealed within the cap is projected from the cap by the released air to provide a visual warning of the tire pressure drop.
U.S. Pat. No. 4,008,744 to Botsis et al. discloses a tire failure indicator that includes a housing mounted in an air tight relation about the tire valve and between the tire valve and the rim valve opening.
U.S. Pat. No. 3,827,393 to Winther discloses an attachment for a pneumatic tire that contains a pressure differential-responsive valve communicating with the interior of the tire and operative to activate a conspicuously decorated signal making unit to cause the unit to be displayed for visual observation when air pressure in the tire for any reason is reduced to a predetermined undesirably low value.
Of the foregoing, only the present inventor's '666 patent provides a tire gauge apparatus which relies on pressure equilibration against a mechanical spring to produce a tire pressure reading (whereby pressurized air entering the valve acts directly on the indicator to oppose a spring force, forcing the indicator to withdraw to a concealed “proper pressure” position). There remains a significant commercial need for this type of pressure equilibration poppet valve which additionally gives a clear, positive indication of a predetermined pressure loss by the exposure of a brightly colored element within a transparent dome, all moving parts of the device being fully enclosed and protected against the ingress of dirt and corrosion by a sealed housing.